Photocurable resins which are transparent or translucent, radioopaque, have good workability, and have good mechanical strength and stability are useful in dental applications, adhesive applications, optical applications, as composites, and in stereolithographic applications.
Low polymerization shrinkage is an important property for such resins. In dental applications, the phrase “zero polymerization shrinkage” typically means that the stresses accumulated during curing do not debond the dentin-restorative interface or fracture the tooth or restorative, which can result in marginal leakage and microbial attack of the tooth. Low polymerization shrinkage also is important to achieve accurate reproduction of photolithographic imprints and in producing optical elements.
Another advantageous property for such resins is maintenance of a liquid crystalline state during processing. For comfort in dental applications, the resin should be curable at “room temperature,” defined herein as typical ambient temperature up to body temperature. Preferred curing temperatures are from about 20° C. to about 37° C. Mesogens which have been found to polymerize in a relatively stable manner at such temperatures are bis 1,4 [4′-(6′-methacryloxyhexyloxy) benzoyloxy] t-butylphenylene mesogens and their structural derivatives. These mesogens have the following general structure:
Unfortunately known synthetic methods for producing these mesogens are costly and have relatively low yields. As a result, the mesogens have enjoyed limited commercial use.
Less costly and simple synthetic methods are needed to produce these mesogens and/or to produce new mesogens that exhibit suitable viscosity for ease in handling, minimal polymerization shrinkage, and relatively high transition temperatures (“Tn->isotropic”).